Vapor lamps utilizing chemical compounds



Oct. 2, 1956 N. c. BEESE ET AL 2,765,416

VAPOR LAMPS UTILIZING CHEMICAL COMPOUNDS Filed sept. 24, 1955 VVVVVVVVU'@ Egg @g3g/QV van VAPOR LAMPS UTILlZlNG CHEMICAL COMPOUNDS Norman C. Beese, Verona, and Donald E. Henry, Cedar Grove, N. l., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Penn- Sylvania Application September 24, 1953, Serial No. 382,110 Claims. (Cl. 313-13) This invention relates to vapor lamps and, more particularly, to those utilizing chemical compounds of metals which have relatively low vapor pressures, in order to increase the vapor pressure and thereby obtain greater eiciency in the generation of invisible radiations of desired wave lengths.

The principal object of our invention, generally considered, is a vapor lamp which efficiently generates invisible radiations adapted to be modulated to a large extent for the transmission of the speech or signals.

Another object of our invention is a lamp in which the ionizable material through which the discharge occurs is free from mercury and selected from the group consisting of the halides of aluminum, bismuth, thallium and tin, excluding the uorides, whereby the spectrum of the desired metal is obtained from material having a higher pressure and exerting less deleterious action on the material of the enclosing envelope.

An additional object of our invention is to produce a vapor lamp, containing the chemical compound of a metal whose spectral emission is desired, `and depending for its :action on the dissociation and recombination of said compound during normal operation.

A further object of our invention is to select such a material in which the metal whose spectrum is desired, combines more readily with the halogen, with which it is combined, than with the material of the envelope, thereby avoiding deleterious attack on the envelope.

A still further object of our invention is to provide a lamp of the character specified containing `a heating element disposed between the lamp and enclosing envelope in order to maintain the temperature of the lamp at the approximate optimum for the generation of the desired radiations.

Other objects and advantages of the invention will become :apparent as the description proceeds.

In the drawing:

Fig. l is an axial sectional view, with parts in elevation, of a lamp embodying our invention.

Fig. 2 is a fragmentary sectional view, with parts in elevation, on the line H-II of Fig. l, in the direction of the arrows.

Fig. 3 is a transverse sectional view on the line Ill*lll of Fig. 2, in the direction of the arrows.

Fig. 4 is :an elevational view, with a part in axial section, of another embodiment of our invention.

Fig. 5 is a graph showing how the optimum temperature of operation varies in accordance with variation in the materials employed.

The present invention is a result of a development to produce a discharge lamp adapted for secret communications. In Patent No. 2,562,887, dated August 7, 1951, there is disclosed such a lamp and an operating system in which cesium vapor serves as the source of near infrared radiation. The lamp of the present application is a variation of that of said patent in that, instead of using cesium vapor as the source of invisible 2,765,416 Patented Oct. 2, 1956 radiations we propose to use a halide of a metal, which metal is so refractory that in elemental form it is not suitable for use in :a discharge lamp, as because of a high boiling point. The materials which we have selected as particularly suitable for the development of invisible radiations of the desired character are the chlorides, bromides, and iodides of aluminum, bismuth, thallium and tin. The uorides are excluded because of the diiiculty in connection with dissociation thereof.

It will also be understood that we generally prefer metal iodides, rather than the other halides mentioned, because they yield relatively higher vapor pressures, that is, of the order of several microns or millimeters of mercury when used in a discharge lamp. Experimental lamps Were made with several metal iodides, using lamp structure generally similar to that of the patent referred to, but suitably modied as will be later explained. All the metal iodide lamps produced radiations that contained the characteristic line spectrum of the metal and a band structure characteristic of the molecule in the chemical compound. The relative intensity of these components varied widely. With some compounds the line spectra were intense and the band structures weak, while with other compounds the band structures possessed most of the radiated energy and the atomic line spectra were of low intensity.

In order to use an iodide or other halide lamp successfully, we were limited to those compounds in which recombination takes place at the operating temperature of the lamp of a rate equal to dissociation. Otherwise, there would be an excess of halogen vapor that would control the discharge, but one is also limited to those chemical compounds where the recombination of metal with iodine or other halogen occurs more readily than the combination of the metal with the material of the envelope. Otherwise, there would again be an excess of free halogen. These factors seriously limit the num- .ber of chemical lamps that can be made into practical devices. Since there is always a loss of some metal to the wall of the enclosing envelope, the heated electrodes probably act as a getter for the halogen, thereby keeping the vapor pressure thereof at a low value.

In connection with making lamps embodying our invention, aluminum iodide was made from the pure elements in vacuum and introduced into a quartz envelope. The discharge was a blue-purple glow that completely filled the envelope with a moderate bulb temperature. At higher temperature the arc constricted to about 1/s of the tube diameter, the voltage became very high, and the ultraviolet output indicated by a zirconium photocell dropped almost to zero. Apparently this compound is easily dissociated and produces an excess Of free iodine :at high envelope temperatures. This accounts for the loss in output and excessive lamp voltage. The principal ultraviolet radiations occurred at wave lengths of 3082, 3092, 3944 and 3961 A. U. An intense band structure occurs with its center near 4500 A. U., and imparts the characteristic color to the discharge. The lamp requires much less external heating for good performance than the thallium iodide lamp later described.

Bismuth iodide lamps have operating characteristic somewhat like the thallium iodide lamps and burned well at 50 milliamperes current for six hours with no visible deterioration. The glow is bright blue with most of the energy in the 4722.2, 4722.5 and 4722.7 A. U. triplet. A group of intense ultra-violet lines generated between 2780 and 3067 A. U. should make this a strong source of erythemal energy.

Thallium iodide was made from the two elements in vacuum and later distilled into a quartz lamp envelope.

This lamp was burned like the others but required a somewhat higher bulb temperature, as compared with the aluminum and tin iodides. With a suitable `ambient temperature and a current of 50 milliamperes, a bright green glow filled the lamp. A zirconium photocell indicated a strong ultraviolet spectrum. This lamp is of a bright green color because the most intense spectral radiation occurs at 5350 A. U. Such a lamp might be developed into a commercial monochromatic source for interferometer work.

A tin iodide lamp gave a strong line spectrum throughout the ultraviolet region down to about 2200 A. U. A diffuse band structure of low intensity extended throughout the range of 3000 to 4700 A. U. This lamp burned with a uniform and steady glow at 30 ma. current and required only a slight amount of heat in addition to the wattage consumed by the discharge.

Now referring to the drawing in detail, like parts being designated by like reference characters, and first considering the embodiment of Figs. l, 2 and 3, there is shown a lamp 11 comprising an inner generally cylindrical envelope 12 bent to U or hair-pin shape and formed of vitreous material, such as quartz or 96% silica glass, so as to readily transmit ultra-violet radiations. The inner envelope 12 is supported inside an outer envelope 13 by lead-in members 14 and 15, extending from the press 16 of the outer envelope 13, and centered therein by means of annular members and 30, which may be like the holding rings 43 and 44 of the Patent No. 2,562,887, referred to. The outer envelope 13 may be formed of material like that of the inner envelope 12 or of vitreous filter material permeable to ultra-violet radiations, but adapted to absorb the visible radiations.

The outer envelope 13 is based, as indicated at 17,

which base is provided with four contact prongs 18, 19,

21 and 22. The prongs 18 and 19 connect with the leads 14 and 15 which, in turn, serve to supply power to the inner envelope 12. The prongs 21 and 22 serve to supply power to a heater element 23, comprising a ceramic or refractory cylinder 24, on which is mounted a coil 25 of Nichrome or other suitable refractory metal wire. The turns of said wire are desirably nonuniformly spaced, that is, more closely spaced towards the electrode-containing ends of the envelope so as to differentially heat the envelope 12 to maintain the electrode-enclosing ends at a higher temperature than the remainder of the lamp. A thermostatic switch 26, supported on the centering member 30, is desirably employed, in series with the coil 2S, to automatically cut it out of the circuit by opening if the optimum temperature is exceeded.

The envelope 12 initially had an extension which was tipped off therefrom, as indicated at 27, after distilling therefrom the halide material selected into the U shape or hairpin portion thereof. The free ends of the envelope have sealed therethrough lead-in conductors 28 and 29,

cach desirably formed of two pieces of tungsten wire respectively connected by the molybdenum foil portions 31 and 32. Each of the electrodes, 33 and 34, consists of a coil of tungsten wire coated with electron-emission material, such as a mixture of the oxides of barium and strontium.

Each electrode is disposed in an end chamber connected to the main portion of the envelope by a passage, 35 or 36, of lesser diameter than the main envelope portion. The halide material distilled into the envelope is admixed with rare gas. As an example a mixture of 5 millimeters of neon and 25 millimeters of argon may be used. During operation, in a typical case, a discharge of 20 to 50 milliamperes is maintained through the envelope 12, amounting to an input of 10 to 40 watts, in the lamp, and up to 50 watts in the temperature-controlling heater element, when the envelope 12 has a diameter of about 6 mm. and a length of about 15 cm. The space between the inner and outer envelopes is desirably evacuated for insulating purposes. s

Fig. 4 shows a modified form of a lamp consisting merely of an envelope 12 unprovided with electrodes, but containing the selected halide material 37, and surrounded by a coil 38 supplied with high-frequency power. Such a lamp avoids electrode corrosion by iodine or other halogen. It is preferably enclosed in an outer envelope, not shown, but like the envelope 13 of the preceding embodiment, except free of metal parts which would absorb energy from the high-frequency field.

Fig. 5 is a graph showing the relative ultraviolet intensity of lamps embodying our invention when halides of dierent metals are employed and the temperature of operation, defined below, varied. The temperature of the coolest part of lamp, i. e. the tip, controls the vapor pressure in the lamp and determines its efficiency. From this it will be seen that the tin halide has the lowest optimum operating temperature of about C., aluminum halide has the intermediate optimum operating temperature of about C., while thallium halide and bismuth halide have the highest optimum operating temperatures of about 265 and 285 C., respectively. It will thus be seen that the thermostatic switch 26 is necessarily differently adjusted when used with lamps having different metal compound fillings in order to obtain the optimum operating results.

Although preferred embodiments have been disclosed, it will be understood that modifications may be made within the spirit and scope of the invention.

We claim:

l. A vapor electric device for the production of radiation within a preselected region of the spectrum comprising an envelope of refractory ultra-violet transmitting material, a vaporizable compound selected from the group consisting of iodides of aluminum, bismuth, thallium and tin, excluding the fluorides, and enclosed in said envelope in a filling of rare gas free from mercury, and means for producing an electric discharge in said envelope.

2. A vapor electric device for the production of radiation within a preselected region of the spectrum comprising an envelope of refractory ultra-violet transmitting material, a quantity of aluminum iodide in a filling of a mixture of neon and argon gases free from mercury, and means for producing an electrical discharge in said envelope.

3. A vapor electric device for the production of radiation within a preselected region of the spectrum comprising an envelope of refractory ultra-violet transmitting material, a quantity of bismuth iodide enclosed in said envelope in a filling of a mixture of neon and argon gases free from mercury, and means for producing an electrical discharge in said envelope.

4. A vapor electric device for the production of radiation within a preselected region of the spectrum comprising an envelope of refractory ultra-violet transmitting material, a quantity of thallium iodide enclosed in said envelope in a neon-argon gas mixture free from mercury, and means for producing an electrical discharge in said envelope.

5. A vapor electric device for the production of radiation within a preselected region of the spectrum comprising an envelope of quartz, a vaporizable compound selected from the group consisting of the iodides of aluminum, bismuth, thallium, and tin enclosed in said envelope in a lling of a neon-argon gas mixture free from mercury, means for producing an electrical discharge in said envelope, an enclosing heat-conserving outer envelope, and means in said outer envelope for maintaining said device at the optimum operating temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,267,858 Ferguson May 28, 1918 1,286,316 Hewitt Dec. 3, 1918 1,925,857 Van Liemp Sept. 5, 1933 

5. A VAPOR ELECTRIC DEVICE FOR THE PRODUCTION OF RADIATION WITHIN A PRESELECTED REGION OF THE SPECTRUM COMPRISING AN ENVELOPE OF QUARTZ, A VAPORIZABLE COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE IODIDES OF ALUMINUM, BISMUTH, THALLIUM, AND TIN ENCLOSED IN SAID ENVELOPE IN A FILLING OF A NEON-ARGON GAS MIXTURE FREE FROM MERCURY, MEANS FOR PRODUCING AN ELECTRICAL DISCHARGE IN SAID ENVELOPE, AN ENCLOSING HEAT-CONSERVING OUTER EN- 